Blower for breathing apparatus

ABSTRACT

A blower for a breathing apparatus has a diffuser for increasing static pressure and/or reducing noise and/or mitigating pressure instabilities and/or managing reverse flow.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

FIELD OF THE INVENTION

The present invention relates to a blower for a breathing apparatus, andin particular to a blower with a diffuser for increasing static pressureand/or reducing noise and/or mitigating pressure instabilities and/ormanaging reverse flow.

SUMMARY OF INVENTION

It is an object of the present invention to provide a blower withimproved static pressure and/or a blower that manages reverse flow.

In one aspect the present invention may be said to consist in blower fora breathing apparatus comprising: a housing with an inlet and outlet, amotor within the housing for rotating an impeller, a diffuser within thehousing between the impeller and outlet, the diffuser comprising a platewith (planar) diffuser elements, wherein the diffuser elements arearranged in cascades on the plate, each cascade comprising a series ofdiffuser elements.

Preferably each diffuser element is offset from adjacent diffuserelements in the cascade.

Preferably the diffuser elements in each cascade are arranged spirallyfrom the perimeter to the centre of the diffuser plate.

Preferably the diffuser elements are aerofoils.

Preferably the blower further comprises a circumferential diffuserelements arranged proximate the perimeter of the diffuser plate todirect airflow from the perimeter of the impeller to the planar diffuserelements.

Preferably the planar diffuser elements in a cascade spiral from acorresponding circumferential diffuser element towards the centre of thediffuser plate.

In another aspect the present invention may be said to consist in ablower for a breathing apparatus comprising: a housing with an inlet andoutlet, a motor within the housing for rotating an impeller, a diffuserwithin the housing between the impeller and outlet, the diffusercomprising one or more circumferential rings with circumferentialdiffuser elements are arranged on the ring(s) to direct air to anoutlet.

Preferably the diffuser elements are arranged in cascades on thering(s), each cascade comprising a series of diffuser elements.

Preferably each diffuser element is offset from adjacent diffuserelements in the cascade.

Preferably the diffuser element cascades are arranged on the innersurface of the one or more rings surrounding the impeller and optionallywherein for each cascade the diffuser elements are arranged in a helicalmanner.

Preferably the diffuser elements are aerofoils.

Preferably the blower comprises an annular ramped wall around theimpeller to reduce flutter.

In another aspect the present invention may be said to consist in ablower according to any paragraph above with multiple diffusers andimpellers.

In another aspect the present invention may be said to consist in ablower for a breathing apparatus comprising: a housing with an inlet andoutlet, a motor within the housing for rotating an impeller, a diffuserwithin the housing between the impeller and outlet, the diffusercomprising diffuser elements, wherein the diffuser elements are arrangedin cascades, each cascade comprising a series of diffuser elements.

Also described is a blower for a breathing apparatus comprising: ahousing with an inlet and outlet, a motor within the housing forrotating an impeller, and a diffuser within the housing between theimpeller and the outlet, the diffuser comprising aerofoil diffuserelements.

Preferably the diffuser elements are arranged in cascades, each cascadecomprising a series of diffuser elements offset from adjacent diffuserelements in the cascade.

Preferably the diffuser element cascades are arranged on a diffuserplate parallel to the impeller, and optionally arranged spirally fromthe perimeter to the centre of the diffuser plate.

Preferably the blower further comprises circumferential diffuserelements arranged proximate the perimeter of the diffuser plate todirect airflow from the perimeter of the impeller to the diffuserelements.

Preferably each spirally arranged cascade spirals from a correspondingcircumferential diffuser element to the centre of the diffuser plate.

Preferably the diffuser comprises a circumferential ring around theimpeller, and the diffuser elements are arranged on the ring thatdirects air to an outlet.

Preferably the diffuser elements are arranged in cascades, each cascadecomprising a series of diffuser elements, wherein each diffuser elementin the cascade is offset from adjacent diffuser elements in the cascade.

Preferably the diffuser element cascades are arranged on the innersurface of one or more rings surrounding the impeller and optionallywherein for each cascade the diffuser elements are arranged in a helicalmanner.

Preferably a blower is provided as above with multiple diffusers andimpellers.

In embodiments, diffuser elements redirect reverse flow such that thereverse flow moves in the same direction as forward flow. This helps toreduce blade pass noise caused by pressure instabilities. When thereverse flow reaches the volute in which the impeller sits, it issubstantially moving in the same direction as the forward flow and caneasily join the stream. Otherwise, a ‘whirring’ sound can be heardbecause reverse flow moving in the opposite direction causes motorslowing/stalling.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the disclosure. Unless specificallystated otherwise, reference to such external documents is not to beconstrued as an admission that such documents, or such sources ofinformation, in any jurisdiction, are prior art, or form part of thecommon general knowledge in the art.

The term “comprising” as used in this specification means “consisting atleast in part of”. When interpreting each statement in thisspecification that includes the term “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting. Where specific integers are mentioned hereinwhich have known equivalents in the art to which this invention relates,such known equivalents are deemed to be incorporated herein as ifindividually set forth. The invention consists in the foregoing and alsoenvisages constructions of which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described with referenceto the drawings, of which:

FIG. 1 shows a perspective drawing of a blower for a CPAP apparatus orsimilar with a diffuser comprising aerofoil diffuser elements accordingto a first embodiment.

FIG. 2 shows a bottom perspective view of a diffuser plate of thediffuser with diffuser elements.

FIGS. 3a, 3b show a top perspective transparent view of the diffusershowing the diffuser elements in a top diffuser plate and diffuserelements between the top and bottom diffuser plates.

FIG. 4 shows a top perspective view of the blower showing forwardairflow from the diffuser elements through an axial outlet.

FIG. 5 shows a top perspective view of the blower showing reverseairflow along the diffuser elements.

FIG. 6a shows reverse airflow on a bottom perspective view of the topdiffuser plate with diffuser elements.

FIG. 6b shows reverse airflow on a bottom perspective transparent viewof the diffuser showing the diffuser elements.

FIGS. 7a, 7b show partial perspective and cross-section views of thediffuser with a flow guide.

FIG. 8 shows a perspective drawing of a multistage blower for a CPAPapparatus or similar with multiple diffusers with diffuser elements.

FIGS. 9a, 9b, 9c show perspective drawings of a blower for a CPAPapparatus or similar with a diffuser comprising diffuser elements in aring according to a second embodiment

FIGS. 10a-10c show a diffuser comprising diffuser elements in a ring infurther detail.

FIGS. 11a-11e show the forward and reverse airflow in the secondembodiment.

FIG. 12 shows a possible impeller.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Axial Inlet/Axial OutletEmbodiment

FIG. 1 shows a blower according to the present invention comprising adiffuser with diffuser elements (in the form of protrusions) that reducenoise, produce the required static pressure from dynamic (airflow)pressure and/or mitigate pressure instabilities and/or manages reverseflow so that reverse flow moves in the same direction as forward flow.The diffuser elements take the form of aerofoils, which promote theCoanda effect. The blower can be used in any suitable breathingapparatus such as a continuous positive airway pressure apparatus(CPAP), bi-level apparatus, autotitration apparatus, high flow therapyapparatus, ventilation apparatus or any other suitable breathingapparatus that would benefit from such a blower. Details of suchbreathing apparatus, and details of how a blower described herein wouldbe utilised in such a breathing apparatus, will be known to thoseskilled in the art, and need not be described here. We refer toPCT/NZ2007/00328 published as WO 2008/056993 as an example, which isincorporated herein by reference in its entirety.

The blower 10 of FIG. 1 is an axial inlet/axial outlet blower. Itcomprises a housing 10 a with an axial inlet 2 for ingress of ambientair, and an axial outlet 3 for outlet of (pressurised) air flow toprovide to a patient either directly by a suitable conduit and patientinterface, or via a humidification apparatus. The blower 10 comprises amotor 4 for driving an impeller 16. The motor 4 could be any suitablemotor for driving an impeller 16 in this type of application, such as(but not restricted to) the low inertia motor described in PCTapplication PCT/NZ2013/000124 published as WO 2013/009193, which isincorporated herein by reference in its entirety. Those skilled in theart will be well versed in the types of motors that could be used, so afull description is not required here, although a brief description willbe provided. The motor comprises a stator 1 surrounding a rotor 6. Therotor 6 is coupled to a shaft 5 that is connected to the impeller 16.The shaft 5 rotates on bearings 9 a, 9 b held in elastomeric mountingdiscs 7 a, 7 b. The discs 7 a, 7 b are coupled to a stator frame 8coupled to the stator 1 to hold the shaft/rotor assembly in a compliantmanner inside the stator 1.

The shaft 5 of the motor 4 extends through an aperture in a shield 12.The shield 12 comprises a flat plate 12 a with an annular wall thatlocates within the housing 10 a, and has an annular channel on itsunderside formed by two protruding walls extending downwards andresiding on the stator 1 of the motor 4. The shaft 5 is coupled to animpeller 16, which resides in the housing 10 a above the flat plate 12a. The impeller is shown in FIG. 13 by way of example, but can take anysuitable configuration such as that shown in PCT/NZ2013/000124 publishedas WO 2013/009193, for example, which is incorporated herein byreference in its entirety.

A diffuser 17 is positioned in the housing 10 a above the impeller 16,and comprises a bottom diffuser plate (diffuser support substrate) 17 aand a top diffuser plate (diffuser support substrate) 17 b. The topdiffuser plate 17 b also forms the top of the housing 10 a to create aninterior volume with the housing 10 a and the flat plate 12 a. The topdiffuser plate 17 b has a central aperture 15. An annular tube 14extends from the central aperture 15, which together form the axialoutlet 3. Dynamic airflow generated by the impeller 16 flows up throughthe diffuser 17 and out through the axial outlet 3.

The diffuser 17 will be described in more detail with respect to FIGS. 2and 3. With reference to FIG. 2, the top diffuser plate 17 b comprises acircumferential/annular wall 21 with circumferential diffuser elementse.g. 20 formed on the internal surface of the wall.

As shown in FIG. 2, each circumferential diffuser element 20 can be inthe form of an aerofoil. The aerofoil takes the form of an aerofoil/wingshape/teardrop shape formed as a vane/protrusion. The aerofoil promotesthe Coanda effect. Aerofoils can be defined by a NACA number and in thepresent invention the aerofoils preferably have a NACA number in the6000-8000 range.

In the preferred embodiment, multiple circumferential diffuser elements20 are spaced evenly around the internal surface of the annular wall 21,although any suitable number or arrangement could be implemented. In amanner to be described in more detail later, airflow generated by therotating impeller 16 passes to the circumferential diffuser elements 20,which direct the airflow up to the gap between the top diffuser plate 17b and the bottom diffuser plate 17 a. Preferably, the number ofcircumferential diffuser elements 20 on the annular wall 21 is prime anddoes not equal the number of impeller blades in order to reducenoise/resonances.

Referring to FIGS. 3a, 3b , the diffuser 17 also comprises furtherplanar diffuser elements e.g. 30 that extend between the bottom diffuserplate 17 a and the top diffuser plate 17 b. Planar diffuser elements onthe top surface of the bottom diffuser plate 17 a can be integrallyformed with the bottom surface of the top diffuser plate 17 b, althoughthis is not essential. The top 17 b and bottom 17 a diffuser plates maybe integrally formed, but that is not essential.

Each planar diffuser element 30 is preferably formed as anaerofoil/wing-shaped/teardrop shaped protrusion/vane promoting a Coandaeffect. Again, the aerofoils preferably have a NACA number in the6000-8000 range. As such, circumferential diffuser elements 20 andplanar diffuser elements 30 formed in this manner can be termed “Coandadiffuser elements”.

Each planar diffuser element 30 (and optionally each circumferentialdiffuser element 20) comprises a rounded leading edge, for example 30 a,with two opposed curved lateral edges, for example 30 b and 30 c, oneconvex and one concave. The two lateral edges, for example 30 b and 30c, converge at and join at a curved endpoint, for example 30 d, in anelongated tail to create the aerofoil shape.

The planar diffuser elements are arranged into a plurality of cascades.Each circumferential diffuser element 20 on the annular wall 21 has acorresponding/respective series/cascade/succession of planar diffuserelements 31 arranged in a cascading manner. The planar diffuser elemente.g. 31 a of a cascade 31 has its leading edge proximate the outlet tailof a corresponding circumferential diffuser element 20 on the annularwall 21. As such, the circumferential diffuser element could also(optionally) be considered part of the cascade. The next planar diffuserelement e.g. 31 b is optionally stepped slightly offset in the X and/orY direction from the tail of the first planar diffuser element 31 a, andeach subsequent planar diffuser element e.g. 31 c in a cascade isoptionally offset in a similar manner from the respective precedingplanar diffuser element 31 b. The planar diffuser elements 31 a-31 c ofeach cascade 31 are arranged and orientated in a manner such that theylie in a curved spiral line 40 (visible in FIG. 4) from the outlet tailof the circumferential diffuser element 20 towards the centre aperture15 of the top diffuser plate 17 b, in a spiral-like arrangement. Thereis a spacing between ea series of spirally arranged planar diffuserelements 31 a-31 c and preferably the spacing increases from narrower towider as the series spirals towards the centre of the diffuser plate 17a.

The bottom diffuser plate 17 a also preferably comprises anannular/circumferential wall with a ramped inner surface 19 (also calleda “wedge”). This provides a recirculation path for impeller airflow toreduce flutter (it “hides” the blade pass). This works in a manner suchas that described in WO2010/126383 filed also by the present applicants.

The operation of the blower 10, and in particular the nature of the airflow in the diffuser 17, will now be described with reference to FIG. 4.As the impeller 16 rotates, airflow is generated at the outercircumference/perimeter of the impeller 16. During forward flow the airis wicked downstream along the gradual sloping aerofoil shape of thecircumferential diffuser elements 20 as indicated by the arrows in FIGS.2 and 3 b. Air enters the gap between the diffuser plates 17 a/17 b fromthe circumferential diffuser elements 20 with a high tangential velocityas depicted by the lighter coloured flow lines e.g. 41 extending fromthe circumference of the blower 10 from the circumferential diffuserelements 20 as shown in FIG. 4. The aerofoil shape of thecircumferential diffuser elements 20 slightly increases the speed ofairflow leaving the ‘tail’ of the circumferential diffuser element 20,which helps the flow adhere to the planar diffuser elements 31 a-31 c onthe top side of the bottom diffuser plate 17 a.

FIG. 4 shows flow lines 41 that demonstrate the (in this case) clockwisemovement of the airflow through the cascades e.g. 31 of planar diffuserelements 31 a-31 c shown on the top side of the bottom diffuser plate 17a (top diffuser plate 17 b removed for clarity). The darkness of theline corresponds to flow velocity, with lighter lines corresponding tolower flow velocities and darker lines corresponding to higher flowvelocities. The Coanda effect gives the airflow a tendency to “stick” tothe outer surface of the aerofoil of a particular planar diffuserelement 31 a-31 c, and the movement along an aerofoil slows down theflow, converting the dynamic pressure of the airflow to static pressure.Additionally, as the airflow moves along the curve e.g. 30 b on thefront of the aerofoil of a planar diffuser element e.g. 30, the flowgains a little extra velocity (due to Bernoulli's principle) (mostvisible, for example, at point E FIG. 4) that can be converted to staticpressure downstream. The diffused flow then collects in the middle andexits the axial outlet 3 at point F in FIG. 4. The gaps between planardiffuser elements 31 a-31 c in a cascade 31 help to promote the Coandaeffect and to promote the tendency for air flow to “stick” to thecascade 31. As the airflow passes from one diffuser element e.g. 31 a toanother e.g. 31 b in a cascade 31, the airflow “re-engages” with thediffuser element, thus promoting airflow to remain closer to the cascade31 of diffuser elements along the entire length. The illustrateddiffuser 17 contrasts with a single continuous spiral diffuser, fromwhich airflow will “detach” from the diffuser much earlier.

FIG. 5 shows flow lines e.g. 50 that demonstrate the movement of reverseairflow from the patient through the aerofoil diffuser element cascadein the blower 10. The diffuser configuration handles reverse flow also.As gases enter the blower from the axial outlet 3, they curve around theaerofoils in such a way that towards the perimeter of the blower 10,they can re-enter the forward stream—not opposed to the rotary motion ofthe impeller 16, but instead aligned with or at least not moving againstthe direction of the rotary motion of the impeller 16. This effect ispromoted by the gaps between each circumferential diffuser elements 20and planar diffuser element 31 a-31 c in a cascade of elements 31 toprovide alternative paths for reverse flow. FIGS. 6a and 6b show light(FIG. 6a ) and dark (FIG. 6b ) arrows similar to those shown in FIGS. 3aand FIGS. 3b , except indicating possible motion of flow lines underreverse flow. As can be seen, the flow lines of FIGS. 5 to 6 b moveroughly in the same tangential direction relative to the impeller 16 asin FIG. 2. This redirection of air flow using the aerofoilssignificantly reduces audible noise resulting in shearing uponexhalation into the blower assembly.

Therefore, the combination of diffuser elements arranged in cascadespirals improves static pressure and provides a path for reverse flow.

While preferably the diffuser elements 20, 30 are aerofoil shaped, thisis not essential. The aerofoil shaped diffuser elements 20, 30 describedin this embodiment are preferable, although not essential. The diffuserelements 20, 30 could simply be used without the aerofoil shape. The useof circumferential diffuser elements 20 in the present invention reducesblade pass noise. The pulsating and unsteady flow stream created bytraditional diffuser vanes is softened by the distance that thesediffuser elements 20 are placed away from the blade tips (proximityreduced).

A wedge 19 also helps in reducing blade tip disturbance in a mannerdescribed above and the aerofoils may take a portion of the velocity inthe annular vortex (phantom impeller) leaving enough velocity there tomaintain a stable source of spinning fluid (gas) to draw from.

Referring to the single stage and multistage blower described below, thegradual negative ‘rake’ or introduction (‘scoop’) to the top layerprovided by the aerofoils is in contrast to other scoops used incentrifugal compressors in that the gradual aerofoil scoop is moreefficient and less disruptive to the main flow stream—thus this scoopcreates less blade pass tonal noise than those other scoops.Additionally the aerofoil shape of the recession/‘tongue’ slightlyincreases the speed of flow leaving the ‘tail’ of the recession, whichhelps the flow adhere to the Coanda effect on the top side of thediffuser plate as described in the next two paragraphs.

The teardrop aerofoil diffuser elements are cascading and are slightlystepped out of place with one another. As the air moves from the Coandarecess onto the plate, the air may still have a tendency to stick to theinside of the aerofoil, but then the air moves across the aerofoil andcollects additional velocity when moving off the ‘head’ of the nextaerofoil (which it strikes because of the stepped nature of theaerofoils)—the additional velocity makes the air more likely to followto the Coanda effect and ride along the outside of the aerofoil. Thecascading aerofoils give the air several chances to change sides, andbecause of this a more even distribution/diffusion of roughly laminarflow lines occurs both along the aerofoils and in between the cascadesof aerofoils.

In the illustrated FIG. 1, flow moving along the planar diffuserelements 30 from the ends of the circumferential diffuser elements 20 tothe central aperture 15 is redirected such that at least a portion ofthe substantially tangential movement of the flow induced by theimpeller 16 is translated into substantially axial movement through theannular tube 14. When changing direction in this space, flow vorticesmay be generated that consume additional mechanical energy (‘shockloss’) and increase the resistance to flow of the gas passageway definedbetween the bottom diffuser plate 17 a and the axial outlet 3.Decreasing the amount of mechanical energy and resistance to flow willminimize pressure loss and decrease the generation of heat and/or noisecaused by such vortices.

In some configurations, and as illustrated in FIGS. 7a, 7b , a flowguide 70 can be placed on the bottom diffuser plate 17 a. The flow guide70 promotes a relatively smooth redirection of flow from the diffuser 17such that shock loss is reduced. As shown in FIGS. 7a, 7b , the flowguide 70 comprises an annular structure beginning at the bottom diffuserplate 17 a. The flow guide 70 is co-axial with the central aperture 15.The annular structure extends towards the annular tube 14 and tapers indiameter towards a point x. The taper of the flow guide 70 increases inseverity along the length of the flow guide 70, imparting to the flowguide 70 a ‘bullet’ or ‘torpedo’ shape. In the shown configuration, theflow guide 70 is integrally formed or in the form of a single continuouspart together with the bottom diffuser plate 17 a.

In some configurations, the flow guide 70 may be horizontally offsetfrom the central aperture 15. In some configurations, the taper of theflow guide 70 may be constant along the length of the flow guide 70. Insome configurations, the average taper of the flow guide 70 along thelength of the flow guide 70 may be 6 or about 6 degrees. In someconfigurations, the flow guide 70 may be a separate component from thebottom diffuser plate 17 a. The flow guide 70 may be joined with thebottom diffuser plate 17 a using other means, including but not limitedto the use of adhesives or welding (e.g. high frequency or ultrasonicwelding). In some configurations, the flow guide 70 may be attached tothe bottom diffuser plate 17 a, top diffuser plate 17 b, and/or annulartube 14. In some configurations, the flow guide 70 may comprise othershapes, including but not limited to columnar, cylindrical, conical,frustoconical or pyramidal shapes.

Additionally, in some configurations, sections of the top diffuser plate17 b defining the central aperture 15 may be bevelled or arcuate insteadof flat or sharp. Smoothing the introduction to the central aperture 15can discourage the formation of flow vortices that lead to shock loss.

It is not necessary for the blower/diffuser to have both circumferentialelements and planar diffuser elements. In one possible embodiment, theblower/diffuser will only have circumferential diffuser elements. Inanother possible embodiment, the blower diffuser will only have planardiffuser elements.

The diffuser 17 described in the first embodiment can be utilised in amultistage blower, such as that shown in FIG. 8. Some means of diffusionis required between stages and a multistage blower can be used toconvert as much dynamic pressure as possible to static pressure so thatsuccessive impellers can impart as much additional dynamic pressure aspossible. Generally, a multi-stage blower system is capable of muchquieter operation than a single-stage blower system, and particularlyfor a wearable CPAP apparatus, the mitigation of stalling sounds duringreverse flow is highly desired because the blower would be much closerto the face than it would be in a non-wearable CPAP system.

The multistage blower shown in FIG. 8 has the same elements as shown inFIG. 1, except that there are multiple impellers and diffusers in series(each stage comprising an impeller and diffuser), with the impeller ofeach stage coupled to the output shaft of the motor. The diffuser andimpeller of each stage have the same configuration as described withreference to FIG. 1. In FIG. 8, a series of four diffuser/impellerstages are shown, but any suitable number of stages could be provided.As shown, a motor output shaft 5 extends through the housing 10 a of theblower 10. A motor 4 is provided at the bottom of the blower 10, aspreviously described in relation to FIG. 1. Stage I comprises animpeller 90 a and first diffuser 91 a. Airflow passing through the firstdiffuser 91 a exits axially through the top diffuser plate into thebottom plate of the next stage where the impeller 90 b of stage IIimparts further energy/velocity into the airflow. The airflow passesthrough the aerofoils of the stage II diffuser 91 b into the diffuserelement cascades 31 of the stage II diffuser 91 b and then out into theimpeller 90 c of stage III and through the stage III diffuser 91 c. Thiscontinues through all the stages until the final stage is reached andthe diffused air from that stage is passed through the axial outlet 3.

Axial Inlet, Radial Outlet Embodiment

In an alternative embodiment, the blower could be in an axialinlet—radial outlet configuration. Referring to FIGS. 9a, 9b and 9c ,the blower 92 comprises a housing 93 including a top plate 94 forming aninterior region within the housing. The top plate 94 has a centralaperture 95 for axial air input, and an outlet 96 radially extendingfrom the housing. Preferably, the outlet 96 is a symmetrical radialoutlet. Namely, the outlet extends radially out along a line “A”extending from the centre of the blower through the perimeter/housing ofthe blower. This contrasts to a more tangential type outlet whichextends from the housing but along a line “B” offset from a centre lineextending from the centre of the blower through the perimeter/housing.An annular wall 97 within the housing creates an annular volute 98, fromwhich the radial outlet extends, and a plate 99 with a central aperture99 a is provided for creating an impeller region within the housing andseparating the motor from the impeller. The motor shaft extends throughthe aperture and connects to an impeller that sits in the impellerregion. A diffuser ring (annular diffuser support substrate) 100 withdiffusion elements e.g. 101 a, 101 b is situated within the volute 98within the housing 93. The diffusion ring 100 can be seen in FIGS. 10a-10 c. The diffusion ring 100 comprises (circumferential/ring) diffusionelements e.g. 101 a, 101 b on the interior surface, the elements/vanesbeing preferably aerofoil shaped, such as described in the previousembodiment. Several diffuser rings 100 can be stacked vertically 101within the volute 98. Preferably the diffuser rings 100 are slightlyoffset (in a similar manner to the planar diffuser elements as describedin the previous embodiment) from one another with respect to theelements 101 a, 101 b to create a sequence of cascading diffuserelements 101 such that moving in an axial direction where each cascadecomprises offset elements that spiral in a helical manner around thecircumference of the impeller on the inner surface of the rings.

In another embodiment they are not separate rings, but rather a singleelongated cylinder (which can still be termed a “ring” or annularsupport substrate) with an inner surface for the elements. This issimilar to the arrangement in the first embodiment, but rather than thecascade of diffuser elements 101 being arranged on a flat plate 17 a ina horizontal plane, the ring/circumferential diffuser elements can bearranged vertically/axially on the interior of an annular surfacecreated from the inner surface of the stacked diffuser rings 100. Theangle between the offset ring diffusion elements 101 a, 101 b in thestack is preferably around 12° as shown in FIG. 10 b.

During operation the motor rotates the impeller, and the impellergenerates an air flow at its perimeter. The high velocity air flow atthe parameter is pulled by the Coanda effect to the diffusion elements101 a, 101 b on the rings and diffused in a similar manner to thatexplained in relation to the first embodiment, except only that the flowis diffused axially rather than radially. The axial diffusion createsstatic pressure and the airflow passes through the radial outlet.

FIGS. 11a , 11 b, 11 c show forward airflow, with lighter colour showinghigh velocity air flow, and darker colour showing lower velocity airflow. As can be seen, high velocity dynamic airflow pressure at theinlet is converted to low velocity static airflow pressure at the outletby way of the diffuser. FIGS. 11d, 11e show reverse flow.

Alternative Embodiments

The embodiments described are not exhaustive of the possibleconfigurations that a blower according to the invention could take.Cascading (preferably) aerofoil diffuser elements of a given size (onthe top of the diffuser plate and/or a diffuser ring arrangement) couldtake other possible sizes, shapes, or configurations. Having a(preferably) aerofoil diffuser element that is too short, or having toomany diffuser elements will reduce the continuity necessary for theCoanda effect to be exhibited, while having an diffuser element that istoo long will allow the boundary layer to stagnate to the effect thatthe Coanda effect will not be seen. Also enough space is requiredbetween the diffuser elements to accommodate the movement of reverseflow in order to bring about the redirection effect depicted. While anaxial inlet/axial outlet blower could be used with a wearable CPAPdevice, this is not preferable as it is awkward. An axial inlet-radialoutlet (relative to the impeller) blower as described in the secondembodiment would be preferred. The feature of the above blower system isseparated diffusion elements that can be cascaded, which can be readilyimplemented in an axial-radial blower system, as described above.

The cascading diffuser element configuration could be used in nearly anyblower type, including but not limited to axial-inlet axial-outlet,axial-inlet radial-outlet, axial-inlet tangential outlet, radial-inletradial-outlet, radial-inlet tangential-outlet, tangential-inlettangential outlet, etc. The teardrop configuration initially discusseddealt with an axial-inlet axial-outlet type blower with diffusionhappening when flow moved over the teardrop plate outwardly to inwardly.Many directions of diffusion are possible as long as the cascadingdiffusion elements are used.

1. A blower for a breathing apparatus comprising: a housing with aninlet and outlet, p1 a motor within the housing for rotating animpeller, a diffuser within the housing between the impeller and outlet,the diffuser comprising a plate with (planar) diffuser elements, whereinthe diffuser elements are arranged in cascades on the plate, eachcascade comprising a series of diffuser elements.
 2. A blower accordingto claim 1 wherein each diffuser element is offset from adjacentdiffuser elements in the cascade.
 3. A blower according to claim 1wherein the diffuser elements in each cascade are arranged spirally fromthe perimeter to the centre of the diffuser plate.
 4. A blower accordingto claim 1 wherein the diffuser elements are aerofoils.
 5. A bloweraccording claim 1 further comprising circumferential diffuser elementsarranged proximate the perimeter of the diffuser plate to direct airflowfrom the perimeter of the impeller to the planar diffuser elements.
 6. Ablower according to claim 5 wherein the planar diffuser elements in acascade spiral from a corresponding circumferential diffuser elementtowards the centre of the diffuser plate.
 7. A blower for a breathingapparatus comprising: a housing with an inlet and outlet, a motor withinthe housing for rotating an impeller, a diffuser within the housingbetween the impeller and outlet, the diffuser comprising one or morecircumferential rings with circumferential diffuser elements arearranged on the ring(s) to direct air to an outlet.
 8. A bloweraccording to claim 7 wherein the diffuser elements are arranged incascades on the ring(s), each cascade comprising a series of diffuserelements.
 9. A blower according to claim 7 wherein each diffuser elementis offset from adjacent diffuser elements in the cascade.
 10. A bloweraccording to claim 6 wherein the diffuser element cascades are arrangedon the inner surface of the one or more rings surrounding the impellerand optionally wherein for each cascade the diffuser elements arearranged in a helical manner.
 11. A blower according to claim 6 whereinthe diffuser elements are aerofoils.
 12. A blower according to claim 1with multiple diffusers and impellers.
 13. A blower according to claim 1comprising an annular ramped wall around the impeller to reduce flutter.14. A blower for a breathing apparatus comprising: a housing with aninlet and outlet, a motor within the housing for rotating an impeller, adiffuser within the housing between the impeller and outlet, thediffuser comprising diffuser elements, wherein the diffuser elements arearranged in cascades, each cascade comprising a series of diffuserelements.
 15. A blower according to claim 7 wherein the diffuser elementcascades are arranged on the inner surface of the one or more ringssurrounding the impeller and optionally wherein for each cascade thediffuser elements are arranged in a helical manner.
 16. A bloweraccording to claim 7 wherein the diffuser elements are aerofoils.
 17. Ablower according to claim 7 with multiple diffusers and impellers.
 18. Ablower according to claim 7 comprising an annular ramped wall around theimpeller to reduce flutter.